c# - Linq 在嵌套集模型中获取直接子级

Question

在 Nested Set Model ，将 sql 转换为 linq 对我来说是一个挑战。

上面的维基百科链接显示了如何按照下面的 SQL 语法列出给定节点的直接子节点，当我使用 LinqPad 对其进行测试时，它运行良好。

SELECT DISTINCT Child.Name
FROM ModelTable AS Child, ModelTable AS Parent 
WHERE Parent.Lft < Child.Lft AND Parent.Rgt > Child.Rgt  -- associate Child Nodes with ancestors
GROUP BY Child.Name
HAVING MAX(Parent.Lft) = 16  -- Subset for those with the given Parent Node as the nearest ancestor

我一直坚持用 LINQ 来表达它，所以我跪下向你学习。

Answer 1

这有效(注意不同的在 SQL 中是多余的):

from c in nodes
from p in nodes
where c.Left > p.Left && c.Right < p.Right
group p by c into g
where g.Max(x => x.Left) == 1
select g.Key;

linqpad 的完整示例:

var nodes = new [] { new {Name = "Clothing", Left = 1, Right = 22} }.ToList();

nodes.Add(new {Name = "Clothing", Left = 1, Right = 22});
nodes.Add(new {Name = "Men's", Left = 2, Right = 9});
nodes.Add(new {Name = "Women's", Left = 10, Right = 21});
nodes.Add(new {Name = "Suits", Left = 3, Right = 8});
nodes.Add(new {Name = "Slacks", Left = 4, Right = 5});
nodes.Add(new {Name = "Jackets", Left = 6, Right = 7});
nodes.Add(new {Name = "Dresses", Left = 11, Right = 16});
nodes.Add(new {Name = "Skirts", Left = 17, Right = 18});
nodes.Add(new {Name = "Blouses", Left = 19, Right = 20});
nodes.Add(new {Name = "Evening Gowns", Left = 12, Right = 13});
nodes.Add(new {Name = "Sun Dresses", Left = 14, Right = 15});

var q =
    from c in nodes
    from p in nodes
    where c.Left > p.Left && c.Right < p.Right
    group p by c into g
    where g.Max(x => x.Left) == 1
    select g.Key;

q.Dump();